When you’re trying to wrap your head around Spanish grammar, the subtle distinctions among verb tenses can make deciding which tense to use tough. Distinguishing between the present subjunctive and the present perfect subjunctive is a case in point. The following guidelines should help you decide which tense is most appropriate:

When the main clause of your sentence expresses doubt or desire in the present or present perfect tense (when something has happened), use the subjunctive in the subordinate clause. Here’s an example:

Yo no supongo que tú leas los mismos libros que yo. I don’t suppose that you (might) read the same books as I.

When the subordinate clause refers to an action that may have (or may not have) taken place, use the present perfect subjunctive in the subordinate clause, as shown in the following examples.

El profesor duda que todos los estudiantes hayan hecho la tarea. The teacher doubts that all of the students have done the homework.